Tactile Warning Surface (TWS) products are required in certain locations under the Americans with Disabilities Act Accessibility Guidelines (ADAAG). The ADAAG defines certain types of applications, including curb ramps/pedestrian crossings, commercial applications (e.g., retailers, hotels and restaurants), institutional applications (e.g., hospitals, universities and schools) and transit facilities (e.g., commuter rail, rapid transit and Bus Rapid Transit (BRT)). The visually impaired may elect to utilize TWS products to detect hazardous drop-offs (platform edge/loading dock) and hazardous vehicular areas (curb ramps on street corners and intersections, uncurbed transition between pedestrian and vehicular areas such as at the front of retail establishments). In addition to the ADAAG, there are several additional documents that offer similar guidelines. These include the Americans with Disabilities Act/Architectural Barriers Act Accessibility Guidelines (ADA/ABA) and the Public Rights of Way Accessibility Guidelines (PROWAG). Most current designs attempt to adhere to all of these guidelines.
Visually impaired and fully sighted persons may rely on a combination of visual cues (color contrast), tactile cues (sweeping cane, sole of shoe, through wheelchair wheels, walker wheels), and audio cues (sound attenuation, which can be achieved by use of dissimilar materials such as composite TWS and concrete substrate) when electing to use TWS products as a means of edge and hazardous vehicular area detection.
TWS products define a series of spaced raised truncated domes. See, e.g., U.S. Pat. No. 7,001,103 for a discussion of TWS products. These products are typically installed in curb ramps, pedestrian ways and commercial, retail and institutional areas by setting into the fresh concrete a plastic, composite or metal TWS product that defines on its upper surface the series of spaced raised truncated domes required by the ADAAG. Although such Cast-In-Place (CIP) TWS products are easy to install into wet concrete (typically taking only a few minutes), replacement is difficult and time consuming, and replacement costs are high, because the underlying substrate must be at least partially destroyed in order to remove an installed product, and then reconstructed for the replacement product.
Some of these CIP TWS Units define a relatively thin upper surface layer supported underneath by spaced honeycomb-like lower walls that are set in fresh concrete. Air can be trapped between the lower walls, which creates areas underneath the CIP TWS Unit that are not supported by the underlying substrate. Because they are thin to begin with, and in spots not supported, these CIP TWS Units can fatigue and crack under moderate or heavy loading, such as can be caused by pallet jacks, fork lifts and vehicles, for example. Also, due to the plurality of intersecting lower walls that are embedded in concrete, in some cases these CIP TWS Units cannot be replaced without tearing up and then rebuilding the concrete structure in which they were set; this is a time consuming and expensive proposition.
Another issue with ADAAG-compliant TWS products is that the projecting domes can be broken or sheared off by snowplows or the like, requiring replacement. Some fiberglass-reinforced epoxy resin TWS products have a body that is reinforced by a woven fiberglass mat. However, the domes are constructed of pure resin without any fiberglass reinforcement for impact resistance. These TWS products thus have projecting domes that are inherently weaker than the body. The domes thus can be more easily cracked, broken or sheared off.
Some CIP TWS Units are set into fresh concrete with fasteners that pass through holes located in the domes. There are also CIP TWS Units in which the head of the fastener is shaped like a dome, in which case the fastener is located in place of one of the domes. In both such cases, if a dome is sheared or broken off, there is danger that the head of the fastener can be sheared or broken off, or at a minimum the fastener can be loosened. If this happens, the TWS product can come loose and present a safety or tripping hazard.
The prior state of the art for new construction includes composite shell CIP TWS Units. Composite shell CIP TWS Units are quickly and economically installed; however, if the installer is not diligent, CIP TWS Units are susceptible to air entrapment underneath the CIP TWS Unit and are thus susceptible to fatigue and cracking failure due to repetitive and/or heavy loading. Fatigue and cracking failure under repetitive heavy loading may also occur along the relatively thin perimeter flange structure. Once installed, CIP TWS Units are permanently embedded into the concrete substrate and it is thus difficult, invasive, time consuming, and costly to remove and replace CIP TWS Units when maintenance is required.
Another solution is a surface applied (SA) TWS panel that is applied to a finished substrate. A SA TWS panel is typically mechanically fastened (e.g., with a nylon sleeve anchor with a stainless steel pin) and adhered (e.g., using single component urethane adhesive) to the underlying substrate, and then caulked around the perimeter to compensate for substrate irregularities, minimize water intrusion, and provide a superior architectural finish. Installation takes 10-15 minutes for a 2′×4′ SA TWS panel. Replacement of a SA TWS panel is easier than with a CIP TWS Unit, and is typically accomplished by removing the fasteners, heating the SA TWS panel to break the adhesive bond with the underlying substrate, prying the TWS panel off the substrate, removing existing adhesive, and installing a new SA TWS panel. The substrate basically remains intact. Perhaps 1 to 1½ hours labor is involved. Replacement cost is thus moderate. However, these SA TWS panels can more easily loosen or dislodge as compared to CIP TWS units. For example, a protruding edge or corner of the SA TWS panel can be caught by a snow plow and lifted. This can present a safety hazard. SA TWS panels may not be as acceptable as CIP TWS Units. SA TWS panels are an ideal solution for retrofit applications; CIP or replaceable (REP) TWS Units are an ideal, quick, and economical solution for new construction. The elevation of the body of a SA TWS panel is at least ⅛″ above the surface of the underlying substrate; consequently, the body of the SA TWS panel is potentially vulnerable to damage from snow removal operations. The body of CIP or REP TWS Units are flush mounted relative to the adjacent substrate; consequently, the body of the TWS Unit is shielded or protected from damage due to snow removal operations. Flush mounted TWS Product installations may offer superior performance when compared to surface mounted TWS Product installations. As the fasteners in SA TWS Panels are located within the truncated dome, they may be vulnerable to damage from snow removal or similar shearing type action that the domes may be subjected to under everyday use.
Many of these TWS products have rectangular top surfaces, typically available in a variety of sizes, including 2 feet by 3 feet, 2 feet by 4 feet, 2 feet by 5 feet, 3 feet by 4 feet and 3 feet by 5 feet. In many applications, a number of TWS products are embedded in the ground to cover a larger area. For example, the edge of a train platform may have a large number of these TWS products to cover a platform that may be fifty of more feet in length.
As described above, to provide tactile warning, a plurality of elevated domes exists on the top surface of the TWS product. The ADDAG sets forth recommended dimensions for these domes. Specifically, the domes should be about 0.2 inches in height, 0.9 inches in diameter, and center-to-center spacing of between 1.6 and 2.4 inches.
FIG. 1 shows a representative rectangular TWS product, showing the size of the product, and the relative positions of the elevated domes on that product. In FIG. 1, the upper surface of a TWS product 10, measuring 2 feet by 4 feet is shown. A plurality of elevated domes 20 is shown on the upper surface. As seen in FIG. 1, each dome has a diameter of 0.9 inches, and is separated from its adjacent domes, in both the horizontal and vertical directions, by 2.4 inches (measured center-to-center).
Note that the elevated domes along the outer edges of the TWS product 10, such as domes 21-25 are 1.2 inches from the edge of the product 10. When two TWS products 10 are placed side by side, the dome 21 of one product is spaced 2.4 inches from dome 23 of the adjacent product, thereby maintaining the ADAAG recommended center-to-center spacing. Note also that corner dome 22 is 1.2 inches from the right edge and lower edge of the product 10. When placed in a configuration with other products, dome 22 will be 2.4 inches from dome 24 of the product below it, and 2.4 inches from dome 25 of the product to its right.
While maintaining proper center-to-center spacing across multiple TWS products is relatively straightforward for rectangular products, this requirement is much more difficult to meet where the TWS products are not rectangular. FIG. 2 shows a representative radial TWS product 30, which are commonly used at crosswalks at intersections. As seen in FIG. 2, the radial TWS product also has domes 40 on its upper surface.
The position of these domes 40 helps illustrate the challenges associated with non-rectangular TWS products. Note that it appears relatively straightforward to maintain center-to-center spacing in the radial direction 50. However the length of row 51 (nearest the inside radius) is less than that of row 52 (nearest the outside radius). Each row follows an arc, which represents a portion of the circumference of a circle. Thus, the length of each row is related to the radius of the circle on which the domes are placed. The rows nearest the inside radius follow an arc of a smaller circle than those of the outer rows. Assume that the inside radius is Ri and the outside radius is Ro. If there is the same number of domes in each row, then the ratio of the center-to-center spacing of the inner row 51 to the outer row 52 can be approximately by Ri/Ro. If each row has the same number of domes, then necessarily, the upper row 52 of domes have a greater center-to-center spacing than those in lower row 51. If the outer radius is 10 feet and the inner radius is 8 feet (assuming a 2 foot wide TWS product), then the center-to-center spacing of the outermost row 52 would be approximately 10/8, or 1.25, of the center-to-center spacing of the innermost row 51. Thus, if the outermost row has a center-to-center spacing of 2.4 inches (i.e. the maximum allowed), the spacing for the innermost row would be approximately 1.92 inches. For different inner and outer radii, the center-to-center spacing for the various rows necessarily changes.
Although not shown in FIG. 2, in some embodiments, the domes 40 are not positioned in radial columns. For example, the domes 40 may be staggered in the radial direction. In addition, the domes 40 may not be arranged in arcs, such as rows 51,52. In some embodiments, the domes may be staggered in this direction.
Radial TWS products are used for various applications, such as pedestrian ramps at intersections. Unfortunately, not all of these applications have the same requirements. For example, in some applications, the outer radius may be required to be 20 feet, while other applications may require outer radii of 10 or 15 feet. To accommodate these various requirements, most TWS suppliers offer a variety of radial TWS products, each product having unique outer and inner radii.
The use of separate radial TWS products for each required radius has benefits and drawbacks. Since each radial product has a specific inner and outer radius, it is straightforward to design the dome pattern to meet the required center-to-center spacing. In addition, it is relatively straightforward to place the domes such that domes on adjacent products also satisfy the ADAAG requirements. However, the use of different radial TWS products also has drawbacks. For example, it is necessary for the supplier to design and manufacture a large number of different parts. This also requires suppliers or vendors to carry inventory of each of these various radial TWS products, thereby increasing inventory costs.
In addition, the existence of multiple radial TWS products complicates the installation process. The installers need to be certain to bring the correct part for the installation. Currently, an existing radial TWS product cannot be used to create a pattern for which it is not intended; there is a strong likelihood that one or more domes would be partially removed, or that the center-to-center spacing would be violated.
Therefore, it would be beneficial if the requirements for various dimensioned radial TWS products could be satisfied by a single radial TWS part, which met the center-to-center spacing requirements for the various configurations.